My "Check Engine" light recently came on and I took my 2003 Toyota Matrix to AutoZone for diagnostics. The computer said that I just need a new oxygen sensor. Not knowing how to do this myself, I took my car to a mechanic with whom I'd had good experiences in the past. He said that the problem was with my Catalytic Converter and that replacement would cost $1300!!

I've seen websites online where I can purchase a Catalytic Converter for my model car for about $365.00. (www.innerauto.com) Could I replace this myself? Should I get a second opinion? My car is no longer under warranty and I would really, really like to not pay $1300 for repairs. Any help or advice is greatly, greatly appreciated! Thanks!